Advertisement

Allele-selective RUNX1 binding regulates P1 blood group status by transcriptional control of A4GALT

Julia S. Westman, Linn Stenfelt, Karina Vidovic, Mattias Möller, Åsa Hellberg, Sven Kjellström and Martin L. Olsson

Key points

  • The intronic A4GALT SNP rs5751348 defines a hematopoietic transcription factor-binding site present in P1 but not P2 blood group alleles.

  • RUNX1 selectively binds to this regulatory site in P1 alleles, and siRNA knock-down of RUNX1 downregulates A4GALT transcript levels.

Abstract

P1 and Pk are glycosphingolipid antigens synthesized by the A4GALT-encoded α1,4-galactosyltransferase, using paragloboside and lactosylceramide as acceptor substrates, respectively. In addition to the compatibility aspects of these histo-blood group molecules, both constitute receptors for multiple microbes and toxins. Presence or absence of P1 antigen on erythrocytes determines the common P1 (P1+Pk+) and P2 (P1-Pk+weak) phenotypes. A4GALT transcript levels are higher in P1 individuals and SNPs in non-coding regions of A4GALT, particularly rs5751348, correlate with P1/P2 status. Despite these recent findings, the molecular mechanism underlying these phenotypes remains elusive. The In(Lu) phenotype is caused by KLF1 haploinsufficiency and shows decreased P1 levels on erythrocytes. We therefore hypothesized KLF1 to regulate A4GALT expression. Intriguingly, P1-specific sequences including rs5751348 revealed potential binding sites for several hematopoietic transcription factors, including KLF1. However, KLF1 binding did not explain P1-specific EMSA shifts and siRNA silencing of KLF1 did not affect A4GALT transcript levels. Instead, protein pull-down experiments using P1 but not P2 oligonucleotide probes identified RUNX1 by mass spectrometry. Furthermore, RUNX1 binds P1 alleles selectively and knockdown of RUNX1 significantly decreased A4GALT transcription. These data indicate that RUNX1 regulates A4GALT and thereby the expression of clinically important glycosphingolipids implicated in blood-group incompatibility and host-pathogen interactions.

  • Submitted August 23, 2017.
  • Accepted January 27, 2018.